The present disclosure relates to a vehicular steer-by-wire system, and more particularly, to a redundant sub-system for providing controllability in the event of a partial system failure.
Modern vehicles are increasingly equipped with sophisticated electronic control systems for achieving finer control. Steer-by-wire is one variety of control system in which the conventional direct mechanical linkage between the input device (e.g., steering wheel or handwheel) and the output device (e.g., steered road wheel) is replaced with a system incorporating electronic input sensors, control circuitry, and output actuators.
In conventional steering assemblies, the operator controls the direction of the vehicle with the aid of a steering wheel. This wheel is typically mechanically connected through a gear assembly to the road wheels. To aid the operator, many systems utilize an auxiliary system to generate a force that is transmitted to a steering gear assembly. The additional force reduces the effort required by the operator in changing the direction of the vehicle. Typically, this auxiliary force is generated by either a hydraulic drive or an electric motor.
One desirable feature of conventional systems is the robust nature of their components. A pending mechanical failure generally exhibits detectable symptoms prior to significant failure. Thus, a feature desirable in a steer-by-wire system is a redundant sub-system to permit continuation of steering control in the case of a sensor failure.
Under the prior art, steer-by-wire systems typically rely on a steering wheel position sensor, the output of which is used to compute a control signal to a road-wheel actuator. Redundancy is typically accomplished with duplicate components, such as duplicate steering wheel position sensors, which improve neither performance nor functionality during normal operation. Accordingly, it is desirable to provide redundancy in a steer-by-wire system without requiring significant duplication of components.
Redundant or fail-safe control of an output device, such as steered road wheels, is provided in the unlikely event of missing or erroneous steering-angle signals from an input device, such as a steering wheel.
The steer-by-wire system includes an input member or steering wheel for receiving the steering inputs made by an operator, a steering-torque sensor connected to the steering wheel for sensing the level of torque being applied by the operator, a control circuit connected in electronic communication with the steering-torque sensor for controlling the actuation of at least one steered road wheel, an output actuator or motor electronically connected to the control circuit for effecting actuation of the steered road wheel, and an output member or tie rod connected between the motor and the road wheel for mechanically translating motor position into road wheel steering angle.